1. Field of the Invention
This invention relates to use in a photothermographic or thermographic material of a coupler containing in the coupling position a carbamoyloxy group ##STR2## that upon oxidative coupling with the a silver halide developing agent, releases a carbamic acid fragment. The carbamic acid fragment, in turn, is capable of thermally releasing ammonia or an amine. The invention also relates to the use of such a coupler with imaging materials that are responsive to ammonia or an amine released upon heating.
2. Description of the State of the Art
Photographic materials for producing silver images and dye images are known. The dye image in such materials is generally produced by a coupling reaction in which a developing agent is oxidized upon development of photographic silver halide in the material, followed by reaction of the resulting oxidized form of the developing agent with a coupling agent to produce a dye image. It has been desirable to provide a means for enhancing an image, that is the silver image or dye image, other than by addition to the photographic material of more coupler, more developing agent and more photographic silver halide. The means for image enhancement according to the invention does not require higher concentrations of such reactants than are otherwise useful.
Couplers which react with the oxidized form of silver halide developing agents are known. Examples of such couplers are described in, for instance, "The Theory of the Photographic Process" edited by T. H. James, 4th Edition, 1977, pages 353-361 and U.S. Pat. No. 3,761,270. None of these couplers in photothermographic or thermographic imaging involve a carbamoyloxy substituent that, upon oxidative coupling with the oxidized form of a developing agent, releases a carbamic acid fragment that, in turn, is capable of thermally releasing ammonia or an amine. The couplers lack the capability of thermally releasing ammonia or an amine.
Imaging compounds that are responsive to or activated by ammonia or an amine are also known. Examples of such imaging compounds are described in, for instance, published patent application WO 80/01322 published June 26, 1980. In such an imaging material phthalaldehyde is an imaging component that forms a dye in response to action by ammonia or an amine released from a cobalt(III) complex. None of these imaging materials contain a coupler, such as a dye-forming coupler, comprising a carbamoyloxy group that is capable of aiding or augmenting imaging upon thermal processing.